Chapter 4 - Making Connections

A)     Interfacing A Computer To Peripheral Devices

a.      Interfacing – the process of providing all the proper interconnections between a computer and a peripheral

b.      Characteristics of interface standards

                                                    i.     De facto standard – a protocol that, although not an official standard, becomes so popular that other companies start using it

                                                   ii.     Electrical component – deals with voltages, line capacitance, and other electrical issues

                                                  iii.     Mechanical component – deals with items such as the connector or plug description

c.      An early interface standard

                                                    i.     RS-232 – the classic example of one of the earliest interfaces

                                                   ii.     EIA-232F – an interface standard for connecting a computer or terminal (or DTE) to a voice-grade modem (or DCE) for use on analog public telecommunications systems

                                                  iii.     Data terminating equipment (DTE) – the computer or terminal end of an interface

                                                  iv.     Data communication equipment (DCE) – the modem

                                                   v.     Full-duplex connection – one in which both sender and receiver may transmit at the same time, EIA-232F is full-duplex

                                                  vi.     Half-duplex connection – one in which either sender or receiver may transmit

d.      Universal serial bus (USB) – modern standard for interconnecting may types of peripheral devices to computers

                                                    i.     Daisy-chaining – connecting a device to each subsequent device (instead of back to the computer)

e.      Other interface standards

                                                    i.     FireWire – type of interconnection between peripheral devices (such as wireless modems and high-speed digital video cameras) and a microcomputer

1.      Asynchronous – supports the more traditional peripheral devices such as modems and printers

2.      Isochronous – provides guaranteed data transport at a predetermined rate

                                                   ii.     Thunderbolt – uses same connector from mini-displayport and provides a 10-Gbps connection to peripheral devices

                                                  iii.     SCSI and iSCSI

1.      SCSI (Small Computer System Interface) (pronounced skuzzy) – technique for interfacing a computer to high-speed devices such as hard disk drives, tape drives, CDs and DVDs

a.      Designed for permanent nature

2.      iSCSI (Internet SCSI) – a technique for interfacing disk storage to a computer via the internet

                                                  iv.     InfiniBand and Fibre Channel

1.      InfiniBand – serial connection or bus that can carry multiple channels of data at the same time. It can support data transfer speed of 2.5 billion bits

a.      It can interconnect thousands of devices using both copper wire and fiber-optic cables

2.      Fibre Channel – serial, high-speed network that connects a computer to multiple input/output devices

a.      Can only support 126 devices only

B)     Data Link Connections

a.      Asynchronous connections – a single character, or byte of data, is the unit of transfer between the sender and receiver

                                                    i.     Sender prepares a data character for transmission, transmit that character, and then begins preparing the next data character for transmission

1.      Frame – small packet of data

2.      Start bit – always a logic of 0, is added to the beginning of the character and informs the receiver that an incoming data frame is arriving

a.      Start bit allows the receiver to synchronize itself to the character

b.      At the end of the data character, one or two stop bits, which are always logic 1s, are added to signal the end of the frame

c.      Finally, a single parity bit, which is inserted between the data bits and stop bit, may be added to the data. This parity bit can indicate either even parity or odd parity, and it performs an error check on only the data bits

                                                   ii.     Slow in data transfer for larger files since there are 3 check bits

b.      Synchronous connections – unit of transmission is a sequence of characters

                                                    i.     Includes a start sequence (flag), a control byte, an address, a checksum, and an end sequence (flag)

c.      Isochronous connections – used to support various types of real-time applications

                                                    i.     Data cannot be too slow or too slow as that could distort and cause buffering for the end user

C)     Terminal-to-Mainframe Computer Connections

a.      Point-to-point connection – single wire runs between two devices and no other terminals or computers share this connection

b.      Multipoint connection – single wire with the mainframe connected on one end and multiple terminals connected on the other end

                                                    i.     Polling – allows only one terminal to transmit at one time, successfully controls multiple terminals that share a connection to a mainframe computer

1.      Primary – a mainframe computer

2.      Secondary – name for each terminal

3.      Roll-call polling – polling method in which the mainframe computer (primary) polls each terminal (secondary), one at a time, in round-robin fashion

4.      Hub polling – polls only the first terminal, which then passes the poll to the second terminal, and each successive terminal passes the poll along

5.      Selection – the primary creates a packet of data with the address of the intended terminal and transmits the packet. Only that specific terminal recognizes the address and accepts the incoming data

D)     Making Computer Connections In Action